U.S. Patent Application Publication No. 2006/0158491 to Belelie et al. discloses non-gellant ink jet ink compositions that comprise wax backbones containing a functionalized group, and methods of forming an image with such inks. Some disclosed ink jet ink compositions are cationically curable.
U.S. Patent Application Publication No. 2006/0158492 to Odell et al. discloses non-gellant ink jet ink compositions that can be cured via at least two different polymerization routes, including radical and cationic polymerization routes, and methods of forming an image with such inks by advantageously utilizing the different polymerization routes. Also described are non-gellant ink jet ink compositions that can be cured by a single polymerization route and that contain two photoinitiator systems that absorb radiation at different wavelengths.
U.S. Pat. No. 7,625,956 to Odell et al., which is incorporated herein by reference in its entirety, discloses a phase change ink composition comprising a colorant, a photoinitiator, and an ink vehicle. The ink vehicle comprises a radically curable monomer compound and an amide gellant compound of the formula
in which the reference further defines the specific substituents.
U.S. patent application Ser. Nos. 12/765,138, 12/765,148, and 12/765,341 to Chopra et al., the disclosures of which are incorporated herein by reference in their entirety, disclose a phase change ink composition comprising a colorant, a photoinitiator, and an ink vehicle. The ink vehicle comprises a radically curable monomer compound and an amide gellant compound of the formula
in which the references further define the specific substituents.
U.S. patent application Ser. No. 12/765,309 to Chopra et al., which is incorporated by reference, discloses a curable ink composition for three dimensional printing comprising an optional colorant and a phase change ink vehicle comprising a radiation curable monomer or prepolymer, a photoinitiator, a reactive wax, and a gellant upon a print region surface, successively depositing additional amounts of the ultraviolet curable phase change ink composition to create a three-dimensional object, and curing the ultraviolet curable phase change ink composition. The ink vehicle comprises a radically curable monomer compound and an amide gellant compound of the formula
in which the reference further defines the specific substituents.
U.S. Patent Application Publication No. 2007/0123606 to Toma et al. discloses a phase change ink comprising a colorant, an initiator, and a phase change ink carrier. The ink vehicle comprises a radically curable monomer compound and an amide gellant compound as further defined in the reference.
Ink jetting devices are known in the art, and thus extensive description of such devices is not required herein. As described in U.S. Pat. No. 6,547,380, incorporated herein by reference in its entirety, ink jet printing systems generally are of two types: continuous stream and drop-on-demand.
In continuous stream ink jet systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. The stream is perturbed, causing it to break up into droplets at a fixed distance from the orifice. At the break-up point, the droplets are charged in accordance with digital data signals and passed through an electrostatic field that adjusts the trajectory of each droplet in order to direct it to a gutter for recirculation or a specific location on a recording medium. In drop-on-demand systems, a droplet is expelled from an orifice directly to a position on a recording medium in accordance with digital data signals. A droplet is not formed or expelled unless it is to be placed on the recording medium.
There are at least three types of drop-on-demand ink jet systems. One type of drop-on-demand system is a piezoelectric device that has as its major components an ink filled channel or passageway having a nozzle on one end and a piezoelectric transducer near the other end to produce pressure pulses. Another type of drop-on-demand system is known as acoustic ink printing. An acoustic beam exerts a radiation pressure against objects upon which it impinges. Thus, when an acoustic beam impinges on a free surface (i.e., liquid/air interface) of a pool of liquid from beneath, the radiation pressure which it exerts against the surface of the pool may reach a sufficiently high level to release individual droplets of liquid from the pool, despite the restraining force of surface tension. Focusing the beam on or near the surface of the pool intensifies the radiation pressure it exerts for a given amount of input power. Still another type of drop-on-demand system is known as thermal ink jet, or bubble jet, and produces high velocity droplets. The major components of this type of drop-on-demand system are an ink filled channel having a nozzle on one end and a heat generating resistor near the nozzle. Printing signals representing digital information originate an electric current pulse in a resistive layer within each ink passageway near the orifice or nozzle, causing the ink vehicle (usually water) in the immediate vicinity to vaporize almost instantaneously and create a bubble. The ink at the orifice is forced out as a propelled droplet as the bubble expands.
Phase change inks, also referred to as hot-melt inks, may be used in ink jet printing. In general, phase change inks are in a solid or semi-solid phase at, for example, ambient temperature, but exist in the liquid phase at the elevated operating temperature of an ink jet printing device. At the jet operating temperature, droplets of liquid ink are ejected from the printing device and, when the ink droplets contact the surface of the recording substrate, either directly or via an intermediate heated transfer belt or drum, they quickly solidify to form a predetermined pattern of solidified ink drops. Phase change inks have been used in other printing technologies, such as gravure printing, as disclosed in, for example, U.S. Pat. No. 5,496,879, the disclosure of which is totally incorporated herein by reference. Phase change inks have also been used for applications such as postal marking, industrial marking, and labeling.
Phase change inks are desirable for ink jet printers because they remain in a solid or semi-solid phase at room temperature during shipping, long term storage, and the like. In addition, the problems associated with nozzle clogging as a result of ink evaporation with liquid ink jet inks are largely eliminated, thereby improving the reliability of the ink jet printing. Further, in phase change ink jet printers wherein the ink droplets are applied directly onto the final recording substrate (for example, paper, transparency material, and the like), the droplets solidify immediately upon contact with the substrate, so that migration of ink along the printing medium is prevented and dot quality is improved.
One problem encountered when preparing ester-terminated polyamide gellants such as those disclosed above is the variability of molecular weight (Mw) distribution of organoamide gellant precursors, which are oligomeric molecules. Variable Mw distribution leads to variability in the gel inks formed during mass production. Variable molecular weight distribution can lead to undesirable variation in the gel strength and viscosity. In particular, the gel may be too soft or too stiff, which can introduce problems in the print process or image quality.
A need remains for improved gellants in phase change inks, for example for gellants that exhibit increased viscosity and a narrow molecular weight range. A need, therefore, also remains for methods of producing gellants with a narrow molecular weight range and control of oligomer size.